Although at first glance this may not be relative to all the ideas that bạn may have about thiên thần and such, let me explain:

The poem is a bout an Angel who got Mất tích in their choices and wants a một giây chance. They want to repent. But to prove that they have changed they must 'capture' a heart, hoặc fall in tình yêu with someone. That person must give up everything for him so that he can go back. They must give their whole tim, trái tim to him. He has ten years to prove that he has changed. And if he doesn't complete this task before his ten years are up, he disappears and leaves nothing behind but a memory.